Fastener



FIG. 1 is a top view of a fastener embodying our new design;

FIG. 2 is a front view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a left side view thereof;

FIG. 7 is a bottom perspective view thereof; 

The ornamental design for a fastener, substantially as shown and described. 